Unoctnilium
Unoctnilium, Uon, is the temporary name for element 180. NUCLEAR What follows is based on a first-order, liquid-drop assessment of where the outer boundary of the nuclear world is. Assume cautious values for how many neutrons a nucleus with 180 protons can bind (high neutron dripline) and how few it can have before it fissions immediately regardless of how much the structure it can develop stabilizes it (low must-fission curve). Assume, too, that anything that lasts long enough so that protons and neutrons can be treated as particles rather than collections of quarks (is causal) might be a nucleus. Under these conditions, Uon isotopes are theoretically possible between Uon 439 and Uon 785 (see "The Final Element", this wiki). Uon 439 through Uon 629 are expected to decay by beta emission if they don’t fission quickly. Above that value of A, the confident neutron dripline, drops may decay by neutron emission before they can fission. (Structural correction does not affect neutron emission.) Uon 629 itself requires 1.5 MeV of structural correction energy to survive for the 10^-14 sec needed to bind an electron and so qualify as a nucleus. Uon 708 and heavier don’t require any correction. Isotopes lighter than Uon 463 need more than twice the correction energy needed to prevent fission in worst-case nuclei in the A = 480 region(1). In between, it is not usually possible to determine whether structural corrections will stabilize nuclear drops against fission. Neutron shell closures have been predicted at N = 406(2),(3),(4), 370(4), 318(5), and 308(1). The isotope Uon 586 requires 2 MeV of structural correction, which means all isotopes in the Uon 576 to Uon 591 band are likely. Uon 550 requires 4 MeV of structural correction, which means some isotopes in the band Uon 540 to Uon 555 are also likely. Long beta-decay half-lives are possible between Uon 540 to Uon 545, so decay by alpha emission is possible in that portion of the band, with beta decay expected in the remainder. Uon 498 requires 13.5 MeV of correction energy and Uon 488 requires 16.5 MeV, which implies that nuclides in these regions are possible only with very strong correction. Between Uon 463 and Uon 660 some drops may be nuclei. Outside this band, isotopes of Uon are nearly impossible. ATOMIC Electron structure of Uon has not been studied closely, but it is likely to differ significantly from the conventional orbitals found in lower-Z nuclei. While only the innermost electrons would be qualitatively different, other electrons are likely to be quantitatively different from those in lower-Z atoms. Uon is also large enough that nuclear shape may have an effect on electron structure, which might cause different isotopes of Uon to have different electronic structures. (That means it is no longer an element in the chemical sense.) Predictions of atomic or chemical properties of Uon are risky. FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. There is a possibility that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Uon 577 and Uon 576 to form. It is probably impossible for lighter isotopes to form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Uon 576 to Uon 591 and Uon 540 to Uon 555 bands. Quantities amount to a few atoms per star at best. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 3. “Search for Superheavy Elements Among Fossil Fission Tracks in Zircon”; J. Maly & D.R. Walz; Stanford Linear Accelerator Center publication SLAC-PUB-2554; July 1980. 4. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 5. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-08-19)